# Building an Image Pipeline

## Setting Expectations

We have a variety of needs when it comes to preserving and
presenting image files to our patrons. Raster images will be
stored in three forms: the archival master, the presentation
master, and a thumbnail.

The archival master will be stored at full resolution in the
original file format. The original file will only be
available to patrons on request. It will not be exposed to
the Internet.

The presentation master will stored in a multi-resolution
image format and be used to generate the images delivered to
our patrons. The presentation master will not be made
available to the patron — they will not be aware that
it exists. Access to the derivatives of the presentation
master will be restricted based on the access rights of the
image.

The thumbnail will be a JPEG scale of the original images
with a 200px longest side. Thumbnails will be made available
to the public for all of our image content _unless_ the
image is explicitly marked private.

### Accepted Formats for Archival Masters
 - DNG
 - JPEG (not recommended for archival masters)
 - PNG[^1]
 - TIFF

### Disallowed Formats for Archival Masters
 - GIF
 - JPEG2000
 - Camera RAW e.g. CR2, NEF, ARW
 - Graphics program formats e.g. PSD, XCF
 - Archaic formats e.g. PICT

### Derivatives Made from Presentation Masters
 - JPEG encoded scale of the image up to 3000px a side
 - JPEG encoded crop of the image up to 3000px a side
 - JPEG encoded tile of a crop or a scale 256px per side
 - JPEG encoded thumbnail 200px per side


## Image Processing

<figure class="illustration"> <figcaption
class="marginnote"> Image Pipeline Block Diagram
</figcaption> <div id="image-pipeline-design"
class="canvas"> <img src="/img/image-pipeline-design.svg"
alt="A line drawing of the components of the proposed image
pipeline."> </div> </figure>

The image pipeline only accommodates raster image files of
particular file types. Other image formats, like EPS, will
be treated as regular files.

[^1]: PNG is the only accepted format that has an alpha channel. There is no plan to preserve transparency in the image pipeline.